469 The Scent of Stimulation: Olfactory Phenomena Induced by Deep Brain Stimulation

INTRODUCTION: Deep brain stimulation (DBS) is an effective therapy for treatment-resistant obsessive compulsive disorder (trOCD), achieving a success rate of 66%. METHODS: A review of intraoperative and programming records from twenty-three trOCD patients treated at Baylor College of Medicine between 2018 and 2024 was conducted. Interviews during programming visits or by phone were used to gather patient experiences of these olfactory events. Stimulation settings linked to olfactory phenomena were extracted from these records. RESULTS: Five patients reported transient phantosmia during sessions. Patient 1 smelled “organic chemistry lab” during bilateral BNST stimulation adjustments. Patient 2 sensed “burning cinnamon” with various settings in bilateral BNST, triggered by changes in pulse width or amplitude. Patient 3 reported a “medical gas” smell during a brief cessation of stimulation. Patient 4 detected a “bad smell” during right VC/VS stimulation with increased amplitude. Patient 5 noticed an unspecified smell when changing contacts. These episodes were consistent and ceased soon after adjusting the stimulation parameters. CONCLUSIONS: The BNST and VC/VS are anatomically proximal to the anterior fascicle of the anterior commissure. We hypothesize that stimulation of these fibers, or a change in stimulation, could facilitate signal transmission to the contralateral olfactory bulb. The transient effects observed here resemble the paresthesias encountered during programming modifications in patients subjected to subthalamic nucleus DBS. This study documents the emergence of phantosmia as a side effect from stimulation adjustments and elucidates the mechanism through which DBS modulates extensive neural networks. It underscores the necessity for further investigative efforts in this domain.